Turbine pump assembly with gas purged centrifugal impeller shrouds

ABSTRACT

Turbine pump assemblies and methods of making the same are provided. The assemblies includes a body, a centrifugal pump having a shroud located within the body, a shroud cavity formed external to the shroud, and a purge gas flow path formed within the body and fluidly connecting a purge gas source to the shroud cavity.

BACKGROUND

The subject matter disclosed herein generally relates to turbine pump assemblies and, more particularly, to turbine pump assemblies having gas purged centrifugal impeller shrouds.

Rockets may be used to launch payloads into space, including inserting payloads into various orbits around the earth or other celestial bodies and/or directing payloads through space. Rockets are maneuvered by vectoring a rocket engine thrust direction. In some configurations, a thrust vector control system may be configured to use hydraulic rams to displace an engine nozzle angle relative to a rocket core axis to control a thrust vector to ensure proper propulsion of a rocket. Hydraulic rams require high pressure hydraulic fluid pumping systems capable of providing, for example, up to 4000 psia at flow rates of 40-100 gallons per minute or greater.

In some systems, the hydraulic flow and pressure may be generated by a turbine pump assembly. The turbine pump assemblies may be powered by hot combustion products, or high pressure cold gas provided by a main engine turbo-pump assembly. Some systems may be configured with a turbine shaft, idler shaft, and output shaft, with a turbine rotational speed controlled by a turbine speed control valve. The turbine speed control valve may operate at speeds that are less than the turbine and may be configured to control flow of fluids to the turbine. In some configurations, the turbine speed control valve may be configured as a flyweight governor actuated spool valve.

Typically, a turbine pump assembly turbine may operate most efficiently at very high rpm (e.g., 115,000 rpm). This is in contrast to a positive displacement hydraulic pump which may operate at significantly lower speeds (e.g., 6100 rpm). To accommodate the differences in operating speed between the turbine and the positive displacement hydraulic pump, a gear reduction system may be incorporated between the positive displacement hydraulic pump and the turbine. For example, a gear reduction system may be utilized to reduce the turbine operating speed (115,000 rpm) down to the positive displacement hydraulic pump operating speed (6100 rpm). The gear reduction system must be geared properly and must be robust enough to transfer power to both the positive displacement hydraulic pump and the valve mechanically linked thereto. Such systems may be large, complex, and expensive.

Such conventional methods and systems have generally been considered satisfactory for their intended purposes. However, improved systems and particularly improved turbine pump assembly systems may provide cost, efficiency, weight, and/or other benefits.

SUMMARY

According to one embodiment, a turbine pump assembly is provided. The assembly includes a body, a centrifugal pump having a shroud located within the body, a shroud cavity formed external to the shroud, and a purge gas flow path formed within the body and fluidly connecting a purge gas source to the shroud cavity.

In addition to one or more of the features described above, or as an alternative, further embodiments of the assembly may include an inner diameter seal and an outer diameter seal, the seals configured to seal the shroud cavity with respect to a liquid fluid path within the turbine pump assembly.

In addition to one or more of the features described above, or as an alternative, further embodiments of the assembly may include that at least one of the inner diameter seal and the outer diameter seal is configured to enable fluid to escape through the respective seal from the shroud cavity.

In addition to one or more of the features described above, or as an alternative, further embodiments of the assembly may include a purge gas transfer tube fluidly connected to the purge gas flow path external to the body.

In addition to one or more of the features described above, or as an alternative, further embodiments of the assembly may include a control section having a turbine gas inlet port, wherein the purge gas transfer tube fluidly connects the turbine gas inlet port of the control section to the purge gas flow path.

In addition to one or more of the features described above, or as an alternative, further embodiments of the assembly may include that the shroud is a first shroud and the shroud cavity is a first shroud cavity, the centrifugal pump having a second shroud and a respective second shroud cavity formed external to the second shroud.

In addition to one or more of the features described above, or as an alternative, further embodiments of the assembly may include that the purge gas flow path formed within the body fluidly connects the purge gas source to the first shroud cavity and the second shroud cavity.

In addition to one or more of the features described above, or as an alternative, further embodiments of the assembly may include a plug configured to plug a portion of the purge gas flow path.

In addition to one or more of the features described above, or as an alternative, further embodiments of the assembly may include that the purge gas source is a turbine exhaust duct.

According to another embodiment, a method of manufacturing a turbine pump assembly is provided. The method includes forming a body and forming a purge gas flow path within the body to fluidly connect a purge gas source to a shroud cavity that is external to a centrifugal pump.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method may include installing a centrifugal pump into the body, the centrifugal pump having a shroud, wherein the shroud defines a portion of the shroud cavity.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method may include installing an inner diameter seal and an outer diameter seal about the shroud, the seals configured to seal the shroud cavity with respect to a liquid fluid path within the turbine pump assembly.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method may include that at least one of the inner diameter seal and the outer diameter seal is configured to enable fluid to escape through the respective seal from the shroud cavity.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method may include supplying pressurized gas through the purge gas flow path into the shroud cavity to expel liquid out of the shroud cavity.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method may include plugging a portion of the purge gas flow path with a plug.

According to another embodiment, a method of operating a turbine pump assembly is provided. The method includes supplying pressurized gas from a purge gas source, passing the pressurized gas through a purge gas flow path, expelling liquid from a shroud cavity around a centrifugal pump with the pressurized gas, and forming a gaseous lubricant within the shroud cavity with the pressurized gas.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method may include that the liquid is expelled around at least one seal.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method may include that the purge gas source is a turbine exhaust duct.

Technical effects of embodiments of the present disclosure include a turbine pump assembly having gas purged centrifugal pump impeller shrouds. Further technical effects include providing a gaseous lubricant within a shroud cavity of a centrifugal pump within a turbine pump assembly.

The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated otherwise. These features and elements as well as the operation thereof will become more apparent in light of the following description and the accompanying drawings. It should be understood, however, that the following description and drawings are intended to be illustrative and explanatory in nature and non-limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter is particularly pointed out and distinctly claimed at the conclusion of the specification. The foregoing and other features, and advantages of the present disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1A is a schematic illustration of a craft that may incorporate embodiments of the present disclosure;

FIG. 1B is an enlarged schematic illustration of a portion of the craft of FIG. 1A;

FIG. 1C is a schematic illustration of a turbine pump assembly for a craft as shown in FIG. 1A;

FIG. 1D is a cross-sectional schematic illustration of the turbine pump assembly of FIG. 1C;

FIG. 2A is schematic illustration of a turbine pump assembly in accordance with an embodiment of the present disclosure;

FIG. 2B is a cross-sectional schematic illustration of the turbine pump assembly of FIG. 2A;

FIG. 3A is an schematic view of flow paths within a turbine pump assembly in accordance with an embodiment of the present disclosure;

FIG. 3B is a schematic illustration showing fluid flow within the flow paths of the turbine pump assembly of FIG. 3A; and

FIG. 4 is a flow process for operating a turbine pump assembly in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

As shown and described herein, various features of the disclosure will be presented. Various embodiments may have the same or similar features and thus the same or similar features may be labeled with the same reference numeral, but preceded by a different first number indicating the figure to which the feature is shown. Thus, for example, element “a” that is shown in FIG. X may be labeled “Xa” and a similar feature in FIG. Z may be labeled “Za.” Although similar reference numbers may be used in a generic sense, various embodiments will be described and various features may include changes, alterations, modifications, etc. as will be appreciated by those of skill in the art, whether explicitly described or otherwise would be appreciated by those of skill in the art.

FIGS. 1A-1D show various schematic illustrations of a craft 10 and components thereof. FIGS. 1A and 1B show schematic illustrations of a craft 10 that may be configured to employ embodiments provided herein. FIGS. 1C and 1D show schematic illustrations of a turbine pump assembly 100 for a craft, such as craft 10, that may employ embodiments disclosed herein

FIG. 1A shows a schematic illustration of the craft 10, which may be a rocket or other space craft. FIG. 1B shows an enlarged schematic illustration of the propulsion system 12 of the craft 10. The craft 10 may include a core booster 14 and may also have additional boosters 16. Each booster 14, 16 includes a body portion 18 extending from a nose portion 20 to a tail portion 22. The tail portion 22 includes the propulsion system 12. The propulsion system 12 includes an engine 24 of the booster. The body portions 18 may contain a liquid or solid propellant to fuel the engine 24 of the respective booster 14, 16. The body portion 18 may also be segmented into multiple booster stages, wherein each stage may contain its own engine. The nose portion 20 may contain, but is not limited to, avionics, payload, and crew compartment, etc. depending on the mission and/or configuration of the craft 10.

As shown, the craft 10 may have a propulsion system 12 that may be configured as one or more rocket engines 24. Each engine 24 may be configured with a nozzle 26 that is configured to direct an output of the respective engine 24. The nozzle 26 thus enables directional control of the thrust of the engine 24 and thus the craft 10. That is, depending on the angle of tilt of the nozzle 26, the craft 10 may be propelled in a specific direction. As such, control of the engine 24 and/or nozzle 26 may be paramount to directional control and safety.

Referring now to FIG. 1B, an enlarged schematic illustration of the propulsion system 12 of the craft 10 according to an embodiment of the present disclosure. The engine 24 may include a combustion chamber and a throat with the nozzle 26 configured thereon to direct exhaust from the throat. Fuel from a respective booster (e.g., boosters 14, 16) is fed into the combustion chamber and ignited. The controlled explosion accelerates as it passes through the throat and out the nozzle 26. This controlled explosion creates the thrust required to propel the craft 10. In order to maneuver the craft 10, the thrust may be directed by a thrust vectoring actuator 28, which physically moves, tilts, translates, rotates, directs and/or adjusts the direction or angle of the engine 24 and/or the nozzle 26 to direct the thrust and thus the direction of movement of the craft 10. As will be appreciated by those of skill in the art, there may be two or more thrust vectoring actuators 28 included on the craft 10, with multiple thrust vectoring actuators 28 configured for each engine and/or nozzle. For example, in some embodiments, two thrust vectoring actuators may be positioned about ninety degrees apart to provide pitch and yaw capability to the craft 10. Accordingly, the thrust vectoring actuators 28 may be provided in operational connection with the engine 24 and/or the nozzle 26. In some configurations, the thrust vectoring actuators may incorporate hydraulic actuators and in other configurations the thrust vectoring actuators may incorporate electromechanical actuators.

Thrust vectoring actuators and related control systems may rely on hydraulic rams to displace the engine nozzle angle, relative to a rocket core axis. The hydraulic rams may require high pressure hydraulic fluid pumping systems capable of providing up to 4000 psia at flow rates of up to 40 gpm. The hydraulic flow and pressure may be generated by a turbine pump assembly. The turbine pump assembly can be powered by hot combustion products, or high pressure cold gas provided by the main engine turbo-pump assembly.

For example, with reference to FIGS. 1C and 1D, schematic illustrations of a turbine pump assembly are shown that may employ embodiments disclosed herein. FIG. 1C is a partial isometric view of a turbine pump assembly 100 and FIG. 1D is a cross-sectional view of the turbine pump assembly 100. The turbine pump assembly 100 is a centrifugal pump based turbine pump assembly having a hydraulic speed control that incorporates a high speed turbine directly coupled to a high speed centrifugal pump. The turbine speed is primarily controlled via a hydraulically driven speed control loop. The turbine speed is modulated by the hydraulic discharge pressure of the centrifugal pump to create a relatively constant hydraulic output pressure that is independent of the discharge flow rate of the hydraulic pump.

Thus, with reference to FIGS. 1C and 1D, the turbine pump assembly 100 includes a turbine/pump section 102 and a control section 104. The turbine/pump section 102 includes a high speed centrifugal pump 106 directly coupled to a turbine shaft 108 of a turbine 110 to generate a desired required hydraulic power within a body 101. A turbine exhaust duct 112 is in fluid communication with the control section 104 by a fluid line 114.

The control section 104 includes a turbine speed control valve 116. A turbine gas inlet port (e.g., as shown in FIG. 2A) may be connected to a valve discharge port, with flow passing through a turbine nozzle housing, a turbine nozzle, the turbine 110, and then into turbine exhaust duct cavity 112. The turbine gas inlet port may be supplied by the rocket or other engine of the craft (e.g., an engine turbo-pump) and/or hot combustion products which may direct high pressure fluid into a first cavity 118 a. The gas passes through the turbine control valve 116 (e.g., decreasing the pressure based on the power need of the turbine 110) and then passes through the turbine nozzles where it is expanded (reducing the pressure to exhaust pressure) thereby increasing the gas velocity.

The turbine speed control valve 116 operates by actuation or movement of a turbine flow rate control spool valve 120 which at one end is in operable communication with a valve opening spring 122 and at another end is in operable communication with a hydraulic piston 124. The hydraulic piston 124 may be a speed control hydraulic piston. Accordingly, the hydraulic piston 124 is in operable communication with a hydraulic pressure tap 126 and a hydraulic pressure feedback line 128.

High pressure fluid may enter the control section at a turbine gas inlet port and enter the first cavity 118 a. The fluid in the first cavity 118 a may be maintained at a high pressure during all operations of use (when the engine is on). The turbine flow rate control spool valve 120 may be moveable within the control section 104 to control fluid flow from the first cavity 118 a to a second cavity 118 b. Fluid pressure within the second cavity 118 b may be controlled by the position of the turbine flow rate control spool valve 120. Further, fluid within the second cavity 118 b may flow through an exit 119 to be directed to a nozzle (not shown).

When the turbine pump assembly 100 is at rest, the valve opening spring 122 forces the turbine flow rate control spool valve 120 open. There is no hydraulic pressure to oppose the valve opening spring 122. In this configuration the valve is fully open, allowing a large propellant mass flow rate to flow through turbine gas inlet port into the second cavity 118 b. As the turbine 110 accelerates, the output pressure from the centrifugal pump 106 increases, providing a large valve closing force to oppose the valve opening spring 122.

As the discharge flow rate of the centrifugal pump 106 increases, the hydraulic discharge pressure also increases. As this happens, the hydraulic pressure in a cavity proximal to the hydraulic piston 124 increases, increasing a closing force acting on the valve spool 120. This additional closing force drives the valve spool 120 toward the closed position (against the valve opening spring 122), decreasing a propellant mass flow entering the second cavity 118 b (and thus airflow through a nozzle), allowing the turbine 110 to slow down, which decreases the operating speed of the centrifugal pump 106, thereby reducing the discharge pressure of the centrifugal pump 106.

As the discharge flow rate of the centrifugal pump 106 continues to increase, a discharge pressure of the centrifugal pump may begin to decline. As this happens, the hydraulic pressure in the cavity of the hydraulic piston 124 may begin to fall, causing a reduction in the force applied by the hydraulic piston 124. As this happens, the valve opening spring 122 may push the valve spool 120 toward the open position, allowing more mass flow to enter the second cavity 118 b and be directed through a nozzle, allowing the speed of the turbine 110 to rise, which may drive the discharge pressure of the centrifugal pump 106 back to a desired value.

The above described and shown turbine pump assembly may be relatively simple and relatively low cost in terms of parts, construction, complexity, etc., there may be efficiency improvement that may be made. For example, when the centrifugal impeller shrouds of the centrifugal pump are rotated at very high speed, while being completely flooded with hydraulic oil, there may be some losses of efficiency. That is, for example, in one non-limiting embodiment, the centrifugal pump 106 may operate at 70,000 rpm, which may result in friction losses associated with first and second shrouds (e.g., a power consumption of 80 horsepower). Without friction losses, a hydraulic reservoir size could be reduced by a factor of two or more.

Accordingly, in accordance with embodiments provided herein, systems and methods of reducing frictional losses in centrifugal pump operation are disclosed. In accordance with one or more embodiments provided herein, a turbine pump assembly is configured to employ high pressure propellant gas and close tolerance labyrinth seals to purge hydraulic oil from first and second shrouds of a high speed centrifugal impeller to reduce frictional losses of the centrifugal pump impeller.

Turning now to FIGS. 2A and 2B, schematic views of a turbine pump assembly 200 in accordance with a non-limiting embodiment of the present disclosure is shown. FIG. 2A shows a partial cut-away view of a control section 204 connected to a turbine/pump section 202. FIG. 2B shows a cross-sectional view of the turbine/pump section 202 of the turbine pump assembly 200. The turbine pump assembly 200 is substantially similar to the turbine pump assembly 100 of FIGS. 1C and 1D, and thus similar features may not be described again.

As shown, the turbine pump assembly 200 includes a control section 204 operably connected to a turbine/pump section 202. The turbine/pump section 202 includes a centrifugal pump 206 having an impeller 206 a with a first shroud 230 and a second shroud 232, with respective shroud cavities defined thereabout (see, e.g., FIG. 3A), within a body 201. The centrifugal pump 206 is operably connected to a turbine shaft 208 of a turbine 210. A fluid line 214 connects a turbine exhaust duct 212 of the turbine/pump section 202 to the control section 204. In some non-limiting embodiments, the first shroud 230 may be a front shroud and the second shroud 232 may be a rear shroud, e.g., based on a fluid flow direction through the centrifugal pump 206.

As shown, a purge gas transfer tube 234 also fluidly connects a part of the turbine/pump section 202 to the control section 204. Specifically, the transfer tube 234 may be fluidly connected with a turbine gas inlet port 218 in order to bleed or receive high pressure gas from the turbine gas inlet port 218 from a purge gas source. The turbine gas inlet port 218 may be fluidly connected to a first cavity 218 a, which, depending on a control and/or position of a valve spool 220, may further be fluidly connected to a second cavity 218 b.

In some embodiments, the purge gas source may be a rocket or other engine of a craft. For example, high pressure turbine propellant gas (e.g., ˜2500 psia) enters the turbine gas inlet port 218 from an engine turbo-pump. As such, gas may pass through the turbine control section 204 (decreasing a pressure based on a power need of the turbine) and then pass through turbine nozzles where the gas may be expanded (reducing the pressure to exhaust pressure) thus increasing the gas velocity. In accordance with embodiments provided herein, a portion of this gas is utilized to supply high pressure gas to the centrifugal pump impeller shrouds 230, 232. The high pressure gas may pass from the turbine gas inlet port 218 and through the transfer tube 234 into one or more purge gas flow paths 236. The gas may purge the shroud cavities of oil and forms a gas or air bearing and/or lubricant.

Turning now to FIGS. 3A and 3B, enlarged views of a turbine pump assembly 300 are shown. FIG. 3A shows a detailed view of the construction of purge paths within a body 301 of the turbine pump assembly 300 to enable high pressure gas to be supplied into shroud cavities of a centrifugal pump, thereby providing a gaseous lubricant that pushes out and replaces an oil lubricant in the shroud cavities.

As shown, a centrifugal pump 306, located within the body 301, includes an impeller 306 a having a first shroud 330 and a second shroud 332. A first shroud cavity 338 is defined between a surface of the first shroud 330 and a surface of the body 301 and a second shroud cavity 340 is defined between a surface of the second shroud 332 and another surface of the turbine pump assembly 300 (e.g., a surface of the body 301 or other component of the turbine pump assembly 300). In a traditional configuration, the first shroud cavity 338 and the second shroud cavity 340 may be filled with hydraulic oil that is discharged from an impeller exit. Fluid may enter the interior of the centrifugal pump 306 at a pump impeller inlet 342 and exit at a pump impeller outlet 344, flowing through an internal fluid cavity 346.

As shown in FIG. 3A, the shroud cavities 338, 340 may be sealed relative to the internal fluid cavity 346 by means of inner diameter seals 348 a, 348 b and outer diameter seals 350 a, 350 b. First inner diameter seal 348 a and first outer diameter seal 350 a may be configured to seal the first shroud cavity 338 and second inner diameter seal 348 b and second outer diameter seal 350 b may be configured to seal the second shroud cavity 340.

In operation, high pressure gas may flow from a purge gas transfer tube 334 into purge gas flow paths 336 formed within the body 301. For example, as shown, gas may flow into a main flow path 336 and separate into a first gas flow path 336 a that is configured in fluid communication with the first shroud cavity 338 and a second gas flow path 336 b that is configured in fluid communication with the second shroud cavity 340. The high pressure gas may then expunge any oil within the shroud cavities 338, 340 past the seals 348 a, 348 b, 350 a, and 350 b. Thus, the shroud cavities 338, 340 may be filled with high pressure gas and any liquid therein may be removed. In some non-limiting embodiments, one or more of the seals 348 a, 348 b, 350 a, and 350 b may be labyrinth seals.

For example, with reference to FIG. 3B, a directional flow path within the turbine pump assembly 300 is shown. Gas may enter at transfer tube 334 and flow into the main purge gas flow path 336 where it may be divided into a first gas flow path 336 a and a second gas flow path 336 b. The gas in the first gas flow path 336 a may flow into the first shroud cavity 338 as shown by the arrows. The gas in the second gas flow path 336 b may flow into the rear shroud cavity 340. From there, the gas will displace hydraulic oil and replace it with the pressurized gas. A small amount of the pressurized gas may leak past the seals 348 a, 348 b, 350 a, and 350 b (as shown by the arrows) and enter the hydraulic oil stream (arrows 352). This gas may be vented from the hydraulic system in an oil-gas separator or in a reservoir. The leakage of the gas past the seals 348 a, 348 b, 350 a, and 350 b enables purging of the oil from the shroud cavities 338, 340, thus leaving only gas within the shroud cavities 338, 340.

FIGS. 3A and 3B also illustrate a manufacturing assembly and formation of the turbine pump assembly 300 in accordance with embodiments described herein. As shown, the flow paths (main flow path 336, first flow path 336 a, and second flow path 336 b) may be drilled or machined after formation of the body 301. Such manufacturing may require plugs 354 configured to plug and seal each of the drilled or machined flow paths. Accordingly, the flow paths as described herein may be formed after formation of the body 301. However, those of skill in the art will appreciate that other manufacturing techniques may be employed without departing from the scope of the present disclosure. For example, molds, casting, and/or additive manufacturing may be used to form a body having the flow paths as described herein.

Turning now to FIG. 4, a flow process 400 for operating a turbine pump assembly in accordance with a non-limiting embodiment of the present disclosure is shown. The flow process 400 may be performed by and with a turbine pump assembly as shown and described above.

At block 402 a high pressure gas may be supplied from a purge gas source. For example, high pressure gas may be supplied from a high pressure gas supply, through a fluid line, and bled therefrom.

The high pressure gas may then be forced or passed through one or more purge gas flow paths that fluidly connect the purge gas source with a shroud cavity, as shown at block 404. The shroud cavity may be located external to a centrifugal pump, and particularly may be formed about a shroud of the centrifugal pump. The shroud cavity may enable lubricant to aid in operation of the centrifugal pump.

As shown at block 406, the high pressure gas that enters the shroud cavity may expel any liquid that is located within the shroud cavity. The liquid may be expelled through or past one or more seals that seal the shroud cavity. That is, the high pressure of the high pressure gas may force any liquid within the shroud cavity to be expunged from the shroud cavity through or past the seals.

As shown at block 408, the high pressure gas may form a gaseous lubricant or gas bearing that passes through the shroud cavity. That is, the gas may replace a liquid lubricant and prevent liquid from entering the shroud cavity. Further, gas may provide lubrication and/or dampening in the seals about the shroud cavity. Accordingly, viscous losses may be prevented by replacing the liquid lubricant with a gaseous lubricant.

Advantageously, embodiments described herein provide a turbine pump assembly that incorporates a high speed turbine, directly coupled to a high speed centrifugal pump. Such configuration may provide improved efficiencies, reduced costs, and other benefits. Further, embodiments provided herein may provide a gaseous lubricant to a centrifugal pump, thus reducing or eliminating viscous drag imparted by a traditional oil-based lubricant. In some embodiments, the turbine may spin at approximately 70,000 rpm, and with an oil-based lubricant, the impeller shroud disk friction may consume nearly 80 horsepower. However, advantageously, embodiments provided herein may reduce the impeller disk friction from 80 horsepower to 10 horsepower by using turbine propellant gas to displace the hydraulic oil in the pump shroud cavities and form a gaseous lubricant. The shroud cavities may be sealed at the impeller ID and OD by seals, maintaining gas within the cavities and preventing oil from entering the shroud cavities.

Moreover, advantageously, embodiments provided herein may enable increased efficiency of a turbine pump assembly. For example, viscous drag on the impeller first and second shrouds may be reduced. The increase in efficiency may decrease propellant requirements of the turbine pump assembly. Furthermore, a required system reservoir volume needed to absorb waste heat energy of the hydraulic system may be decreased.

While the present disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to such disclosed embodiments. Rather, the present disclosure can be modified to incorporate any number of variations, alterations, substitutions, combinations, sub-combinations, or equivalent arrangements not heretofore described, but which are commensurate with the scope of the present disclosure. Additionally, while various embodiments of the present disclosure have been described, it is to be understood that aspects of the present disclosure may include only some of the described embodiments.

For example, although shown with flow paths configured to supply high pressure gas to both the first and second shroud cavities, those of skill in the art will appreciate that high pressure gas may be provided to only one of the two shrouds without departing from the scope of the present disclosure. Further, although shown with the purge gas transfer tube joining the main flow path at a ninety degree angle, those of skill in the art will appreciate that the purge gas transfer tube may join and supply gas to the shroud cavities in any configuration. For example, the purge gas transfer tube may connected to the main flow path at the end of the flow path (e.g., shown to the right side in FIG. 3B).

Accordingly, the present disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims. 

What is claimed is:
 1. A turbine pump assembly comprising: a body; a centrifugal pump having a shroud located within the body; a shroud cavity formed external to the shroud; and a purge gas flow path formed within the body and fluidly connecting a purge gas source to the shroud cavity.
 2. The turbine pump assembly of claim 1, further comprising an inner diameter seal and an outer diameter seal, the seals configured to seal the shroud cavity with respect to a liquid fluid path within the turbine pump assembly.
 3. The turbine pump assembly of claim 2, wherein at least one of the inner diameter seal and the outer diameter seal is configured to enable fluid to escape through the respective seal from the shroud cavity.
 4. The turbine pump assembly of claim 1, a purge gas transfer tube fluidly connected to the purge gas flow path external to the body.
 5. The turbine pump assembly of claim 4, further comprising a control section having a turbine gas inlet port, wherein the purge gas transfer tube fluidly connects the turbine gas inlet port of the control section to the purge gas flow path.
 6. The turbine pump assembly of claim 1, wherein the shroud is a first shroud and the shroud cavity is a first shroud cavity, the centrifugal pump having a second shroud and a respective second shroud cavity formed external to the second shroud.
 7. The turbine pump assembly of claim 6, wherein the purge gas flow path formed within the body fluidly connects the purge gas source to the first shroud cavity and the second shroud cavity.
 8. The turbine pump assembly of claim 1, further comprising a plug configured to plug a portion of the purge gas flow path.
 9. The turbine pump assembly of claim 1, wherein the purge gas source is a turbine exhaust duct.
 10. A method of manufacturing a turbine pump assembly comprising: forming a body; and forming a purge gas flow path within the body to fluidly connect a purge gas source to a shroud cavity that is external to a centrifugal pump.
 11. The method of claim 10, further comprising installing a centrifugal pump into the body, the centrifugal pump having a shroud, wherein the shroud defines a portion of the shroud cavity.
 12. The method of claim 11, further comprising installing an inner diameter seal and an outer diameter seal about the shroud, the seals configured to seal the shroud cavity with respect to a liquid fluid path within the turbine pump assembly.
 13. The method of claim 12, wherein at least one of the inner diameter seal and the outer diameter seal is configured to enable fluid to escape through the respective seal from the shroud cavity.
 14. The method of claim 10, further comprising supplying pressurized gas through the purge gas flow path into the shroud cavity to expel liquid out of the shroud cavity.
 15. The method of claim 10, further comprising plugging a portion of the purge gas flow path with a plug.
 16. A method of operating a turbine pump assembly comprising: supplying pressurized gas from a purge gas source; passing the pressurized gas through a purge gas flow path; expelling liquid from a shroud cavity around a centrifugal pump with the pressurized gas; and forming a gaseous lubricant within the shroud cavity with the pressurized gas.
 17. The method of claim 16, wherein the liquid is expelled around at least one seal.
 18. The method of claim 16, wherein the purge gas source is a turbine exhaust duct. 